Soil physical properties change in the process of oasisization

Online system, http://www.scar.ac.cnSciences in Cold and Arid Regions2010, 2(4): 0345- 0353Science PressSoil physical properties change in the process of oasisizationHui Wang, WenZhi Zhao 2, LiShan Shan1. Collge of Forestry, Gansu Agricultural University, Lanzhou, Gansu 730070, China2. Linze Inland River Basin Research Station, Laboratory of Basin H)ydrology and Ecology; Cold and Arid Regions Environmentaland Engineering Research Institute, Chinese Academry of Sciences, Lanzhou, Gansu 730000, China*Correspondence to: Hui Wang, College of Forestry, Gansu Agricultural University. NO 1, Yingmen Village, Lanzhou, Gansu730070, China. Email: wanghui@lzb.ac.cnReceived: 11 January 2010 Accepted: 28 April 2010ABSTRACTOasisization is a process of converting a natural desert into a man-made oasis in order to satisfy social needs under certain eco-nomical and technical conditions. This paper subtutes space for time in order to study physical property changes of oasis soilalong the oasisization in about a 1,000-year period. This research focuses on providing the bases for better understanding theprocess of oasiszation. The results show: (1) In about 1,00-year chronological scale, the bulk density and the saturated soil hy-draulic conductivity of the surface layer (0- 20 cm) significanty reduced with the increase of land reclamation time, while soil po-rosity, stability of aggregates, and silt content significantly increased. The soil bulk density of the unreclaimed filed (0 year) andthe reclaimed field (about 1,000 years) in the surface layer (0- -20 cm) are 1.51 g/cm3 and 1.35 g/cm', the total porosity are 43.16%and 49.27%, the apilary porosity are 38.73% and 47.10%, the water stable aggregate (<>0.25 mm) content are 24.60% and49.59%, the sand content are 85.42% and 61.56%, the clay content are 3.93% and 4.80%, the specific surface area are 128 cm/gand 231 cm-/g, and the saturated hydraulic conductivity are 0.74 cm/h and 0.34 cm/h, respectively. (2) In the first 30 years of theoasis reclamation, the changes are relatively fast, and the rates of the saturated soil hydraulic conductivity, dry aggregate (>0.25mm), water-stable aggregate (>0.25 mm) content, and specific surface area are 0.01 cm/h:yr, 0.58%/yr, 0.50%/yr, and 1.48 cm2/gyr, respectively.Keywords: oasisization; bulk density; aggregate; clay; saturated hydraulic conductivityGuo et al, 2007). Some researchers focus on the evolu-1. Introductiontional characteristics of coarse-grained soil, loss of nutri-ents, and deterioration of soil environment in land degra-dation processes in different spatial and temporal scalesinto a man-made oasis to satisfy social needs under certain(Zhao et al, 1996, 2002, 2005; Xiao et al., 1998; Liu et al.,economic and technical conditions (Jia and Ci, 2003). An2000; Fan et al, 2002; Zeng and Feng, 2008). The recon-important consequence of oasisization is that soil qualitystruction and fertilization of oasis soil includes the processimproves which can be characterized by changes in soilof irigation-siltation and farming -developing. Therefore,physical properties. Numerous studies have recently beenthe study of irrigation-silted soils became an importantcompleted that focuses on the influence of vegetation re-aspect of oasis soil research (Chen, 1982; Wang, 1984; Shicovery or different land-use patterns on soil physical prop-and Gu, 1991; Shi and Gong， 1992). It has been wellerties (Zhang et al, 1997; Wu and Hong, 1999; Fu anddocumented that irrigation-silted soils can be divided intoChen, 2000; Li and Xie, 2001; Su et al, 2002; Fu et al,common irigati中国煤化rigationsited2003; Stolte et al, 2003; Wen et al, 2004; Ma et al., 2005; .soil and hydroposub-categoryYHCNMHG346Hui Wang et al, 2010/ Sciences in Cold and Arid Regions, 2(4): 0345- 0353of agriculural use in the Hexi Corridor of China (Chen etand the windy seasons are from April to May, with an annualal, 1993; Li, 1995). The irigation-sited soil can be di-wind velocity of 3.2 m/s, maximal velocity of 21 m/s. Gen-vided into the processes of irigation siltation, farm-erally, the average heavy windy period is about 15 daysing-fertilization, and irigation-leaching (Li et al, 1999). Inevery year.' I he main climate characteristics are drought,the past decade, great interest has been focused on the 0a-high temperatures, and windy. The zonal soil is gray-brownsis soil, including Luo et al. (2005) who studied the effectdesert soil and some azonal soil, for example, irriga-of different land-use systerms on soil properties of an Allu-tion-silted, saline, fluvo-aquic, mire, and sandy soils.vial Plain-oasis in an arid landscape. They found that sandThe landscape of the study area is composed mainly oftended to decrease with increasing time of land cultivation,the oasis and the desert, which is the essence of the Heiheand silt and clay trended to increase in the oasis soil. Xu etRiver Basin. Human activities have severely impacted theal. (2006) analyzed the spatio-temporal variability of soilnatural ecosystems, which significantly aected the soil. Theorganic C and nutrients in the oasis of the norther slope ofoasis is located in the central and southerm areas, with theGobi desert and the southerm edge of the Badain Jaran Deties in the oasis were reasonable and the environment ofsert located in the northern areas. In the last half of the 20hthe oasis was improved. Pan et al. (2005) and Zhang et al.century, the amount of reclaimed land in this area has more(2006) studied the succession trend of soil quality afterthan doubled compared to the region's population growthreclamation of an oasis in the Manasi river valley, anrate and large-scale development and construction. The cur-found that with the increase of reclamation time, therent population in this area is 123.4 million, and the per cap-salt-loving, perennial plants were substituted by annualita arable land is 0.196 hm'. Desert vegetation is dominatedplants and then entered a stable stage after 6- -8 years. Theby xeric shrubs and semi-shrubs such as Salsola passerinasynthetic analysis of various indices of soil quality indi-Bge. (Salsola: Chenopodiaceae), Reaumuria soongaricacates that 10-15 years could be used as an early-warming Maxim. (Reaumuria: Tamaricaceae)， Nitraria sophaero-time to reflect the change of soil quality. However, there iscarpa Maxim. (Nitraira: Zygophyllaceae), Polygonaceae,little information about researching the process of oasisiza-Ephedraceae，Asteraceae, Leguminosae and Gramineae.tion through change of soil physical properties.Community coverage is generally not more than 30%. Arti-An oasis resides in the desert but is different from theficial protective vegetation of the oasis is dominated bydesert. Under certain conditions, an oasis can be transformedpoplar and Elaeagnus cangustifolia L, and the main crops arefrom one form to another as "desert oasisization" or "oasiswheat and corn.desertification." Therefore, we hypothesize that the devel-opment and stability analysis of an oasis system are signifi-cantly affected by soil physical properties in a particular area2.2. Field investigation and samplingIn this study, we use the method of utilizing space instead oftime to study the changing process of physical properties ofIn order to verify ages of land reclamation (mainlyS30an oasis soil, an oasisization that occurs within a 1,000-yearperiod in an arid region of northwest China. This researchyears) and to reduce the margin of error, an investigationwas conducted in the study area, including interviews withfocuses on providing the bases for better understanding thefarmers or their offspring. During the interviews, a series ofprocess of oasisization.questions were asked, including a comparison of the age ofthe farmer's offspring and the reported land cultivation time.2. Materials and methodsTherefore, reclamation durations of less than 30 years wererelatively precise. For reclamation durations longer than 30years, the exact times were mainly estimated according to2.1. Description of the study areathe literature, including agriculture, water conservancy, so-cial and historical. In this study, seven sites were selected inThe study area is located in the middle of the Heihethe vicinity of the Linze inland river basin research station inRiver Basin in Zhangye, Gansu Province, including thethe northern Zhangye city (Table 1).counties of Linze, Gaotai, Minle, and Shandan. The geographi-Soil samples were collcted in July 2006 before au-cal coordinates are 37*28' -39°57'N and 97°20'- -10212'E. It is tum irrigation. Three replicates were selected in eacha typical desert oasis which mainly relies on the Heihe River; sampling plot. Within each sampling plot, three 10mx 10mtherefore, it belongs to an arid desert climate. The meansampling locations spaced at least 100 m from each otherannual temperature is about 7.4 8.5 °C; the mean annualwere demarcated and regarded as field replicates. At eachprecipitation is 108- 478 mm, with nearly 70- -80% fallinglocation in each treatment, the soil samples (0- 20 cm depthbetween May and September; and the yearly mean evapora-and 20 40 cm depth) were collcted from 3 points by ation is 1,341- 2,388 mm. The average total length of sunlightsoil auger, mixed and pooled as one composite sample. Inis 3,000 4,000 hours annually. The annual cumulative tem-addition, 3- -6 soil cores (stainless steel cylinders with aperature of≥10。C is around 3,088。C and the frost-freevolume of 100中国煤化icatio for soilperiod is 165 days. The main wind direction is northwest,bulk density andMHCNM HGHui Wang et al, 2010 1 Sciences in Cold and Arid Regions, 2(4): 0345- -0353347able 1 Land cultivation histry, geographical coordinates, and agriculture utilization history of sarmpling plotsDuration (years) ofGeographic coordinatesAgriculture utilization historyreclamation03924"3.9"N; 100973.7"EVirgin3923'31"N; 100*6/57.8"E20392248. 5"N; 10096'53.1"EPlanting wheat and corm in the past.3922'48"N; 1009658"EPlanting breeding corm in recent years.about 10039183.9"N; 10095'32.3"Eabout 50039*9'58'N; 1001024.6"EPlanting wheat, corm and other crops in the past.about 1,00039337.6"N; 100^1521.5"E2.3. Laboratory analysis3. Results and discussionSoil physical properties were determined by general3.1. Bulk density and porositymethods in the lab (ISSCAS, 1978; Yan, 1988; Sun and Liu,1996). Soil samples were air-dried and hand-sieved throughTable 2 shows that the bulk density of the surface layera 2-mm screen to remove roots and other debris. Bulk densi-(0- 20 cm) reduces when the oasis soil developing and landties were determined by oven-drying cores at 105-110。Cafter porosity and water-holding capacity measurementsreclamation years increase, but for the subsurface soilwere completed. Particle size distribution was determined by(20- 40 cm) there is no evident trend. The bulk density ofthe pipette method in a sedimentation cylinder. Aggregateunreclaimed field (0 year) in the surfacc and subsurface lay-stability measurements were performed on initially air-drieders are 1.51 g/cm3 and 1.52 g/cm', respectively. The bulkaggregates. Aggregate stability was evaluated according todensity of reclaimed field (for about 1,000 years) in the sur-face layer is 1.35 g/cm', and in the subsurface layer is 1.48wet-sieving efects. Soil saturated hydraulic conductivitywas measured by the tension infiltrometer. Soil specific sur-g/cm'. The soil total porosity and capillary porosity trend inface area (SSA) is a property that synthesizes mechanicalthe surface and subsurface layers are opposite to the trend ofcomposition characteristics. SSA was calculated usingthe soil bulk density, both of which increase with the in-Equation (1) for sand (2- 0.05 mm), sit (0.05 -0.002 mm),crease of soil reclamation. However, the tendency in thesubsurface is not as obvious as that in the surface. The soiland clay (<0.002 mm) fractions (Foster e1 al, 1985):total porosity of unreclaimed field (0 year) surface layer isSSA=0.05(Sa%)+4.0(Si%)+20(Cl%) (1) 43.16%, and that of the oasis afer relamation of about1,000 years is 49.27%。The soil capillary porosity of unre-where Sa, Si and CI are the percent of sand, silt, and clay inclaimed surface soil is 38.73%, and after 1,000 years recla-the soil, respectively.mation it increases to 47.1%. In addition, the ratio of soilIn total, 378 soil samples were cllcted (7 stagesx3 cpilay porosity and total porosity increases with the in-sitesx3 plotsx3 measurementsx2 layers) for all items.crease of soil reclamation year.Soil bulk density, porosity, and distribution can reflectthe soil structure and affect the variation and coordination2.4. Statistical analysisof fertility factors such as soil, water, fertilizer, gas, andheat (Chen, 1990). Due to oasisization by way of rrigationMicro-excel and SPSS 13.0 were used to analyze theand fertilization, soil changes from desert soil to oasis soil,data. Although the experiments were pseudo-replicate, it resulting in an improvement of the soil structure. This pro-can be considered that the sampling distance between rep-duces a change in soil physical properties, including thelications was sufficient to ensure adequate variation esti-decrease of soil bulk density, increase of total porosity andmation within each site. One-way analysis of variancecapillary porosity, and enhancement of water-holding ca-(ANOVA) and Duncan's test were carried out using thepacity. The time gradient of seven different reclaimed ageSPSS 13.0 procedures for sites in different successionshow that soil bulk density gradually decreased, but thestages. Duncan's test was used to compare means of soilevolution of soil total porosity and capillary porosity in-variables when the results of ANOVA were significant atcreased. Therefore, the study of soil bulk density, total po-p<0.05. The correlation of soil physical properties was rosity, and capi中国煤化工the oasis soildescribed by correlation analysis.gradually develosization whenMYHCNMHG348Hui Wang et al, 2010/ Sciences in Cold and Arid Regions, 2(4): 0345- 0353the soil structure has improved and the water -holding andare conducive to the growth of plant roots and the cultiva-fertilizer-conserving capacity have become stronger, whichtion of crops.Table 2 Bulk density, total porosity, and capillary porosity in the surface (0- -20 cm) and subsurface (20 40 cm)soil layers of different reclamation yearsDuration (years) ofBulk density (g/cm)Total porosity (TP, %)reclamation0- 20 cm20- 40 cm0- -20cm20 40 cm1.51*(0.07)1.52(0.10)43.16(2.53)42.80*(3.81)1.476*(0.6)1.47b<(0.10)44.53h<(2.29)44.54*(3.77)01.43*(0.07)1.41*(0.06)46.08*(2.60)46.84(2.06)1.50*(0.09)43.46*(3.46) .46.18*(2.78)about 1001.62*(0.05)1.64(0.08)38.84(1.73)38.11(3.00)about 5001.41(0.06)1.62(0.10)47.02*(2.04)38.78*(3.59)about 1,0001.359(0.05)1.48*(0.06)49.27*(1.71)44.20*(2.14)Capillary porosity (CP, %)CP/TP(%)20-40cm_38.730.46)35.56*(5.33)88.74*(4.82)81.89(4.18)39.10*0.85)4071*(2.25)88.36*(2.65)90.76*(2.32)4077(0.48)42.48*(3.46)89.26<4.62)90.36*(3.06)3(40.26*(3.52)43.29(3.98)89.78*(1.81)95.12(3.31)34.24(1.22)33.91(1.41)86.48*(1.96)86.36*(4.31)41.15*(0.84)34.71%(3.42)85.48*(4.40)87.15<(2.93)47.10(2.37)43.02*(0.48)97.06*0.51)96.13*(4.87)Means with the dfferent ltter in the same row are significantly diferent (ρ<0.05) (Duncan's test); Data in the parentheses are standarddeviations.of aggregates (>0.25 mm) significantly reduced, and aggre-3.2. Change of aggregatesgates >5 mm reduced most significantly. During the waterdamage, aggregates >5 mm of all samples reduced to 0,The dry aggregate (>0.25 mm) content of the surface soilwhich indicates that water-stable aggregates are significantlylayer (0 -20 cm) increased with the increase of oasis soilaffected by farming activities. The water- stable aggregatereclamation years (Table 3). The dry soil aggregate content(>0.25 mm) content of different cultivation years range fromat the reclamation period of 20 years is relatively high, with4.89% to 49.59%, and the aggregate structural destructionthe average content of soil dry-sieving aggregate at a size ofrate ranges from 37.07% to 92.07% after wet sieving, which>0.25 mm is 91.13%, mainly in large particle size. The av-indicates that water-stability of these aggregates differs sig-crage content of soil dry-sieving aggregates of>5 mm, 5- 2 nificantly. This is the reason why the oasis in different culti-mm, 2-1 mm, 1-0.5 mm, and 0.5- 0.25 mm are 34.60%,vation years has significant diferences in soil corrosion re-23.67%, 10.13%， 12.47%, and 10.27%, respectively. Thissistance and soil moisture preservation ability. The structuralsuggests that dry aggregates at every level are unevenly dis-destruction rates of the oasis soil, which has been reclaimedtributed. The higher the large size aggregate content is, thefor 7 years and 30 years, are 90.69% and 92.07%, respec-better the aggregation. The difference of the dry soil aggre-tively. It indicates their poor stability, and the majority of soilgate (>0.25 mm) content between seven years reclamationaggregates will be broke down after moisten. In addition, theand unreclaimed soil is not obvious, and the value is aboutstructural destruction rate of the oasis soil after reclamation50%; the content of dry aggregate (>0.25 mm) in the other of about 1,000 years is 37.07%, which indicates that duringfive oasis soils (>seven years reclamation) varies lttle, rangethe development of the oasis soil, the soil structure has to gofrom 78.80% to 91.13%.through a very long stretch of time before stabilizing.Dry-sieving results in dry aggregates, and wet-sievingTable 3 shows that the reclamation age affects not onlyresults in water-stable aggregates. The difference between the composition of aggregates at the surface soil layer, butthe two methods reflects the degree of influence of solublealso the characteristics of soil aggregates at the subsurfacesalt, which play a key role in the formation of an aggregatelayer. Results show that water-stable aggregate <>0.25 mm)and the stability mechanism. As to the surface soil layercontent decline中国煤化工about 1,000(0- 20 cm) samples processed by water damage, the numberyears > about 5020 years> 30YHCNMHGHui Wang et al, 2010/ Sciences in Cold and Arid Regions, 2(4): 0345- 0353349years > 7 years, ranging from 2.32% to 23.33%. Generally,production of crops (Yan, 1988). From studies on thewater- stable aggregate (>0.25 mm) content reflects an in-changes of oasis soil aggregates of different cultivation years,crease trend with the increase of reclamation years of thewe can see that the process of oasisization is also the processoasis soil.of the formation of aggregate structure and gradual im-stances are the basic structure of the soil unit. Their quantitywater-stable aggregate (<>0.25 mm) content increases, whichand quality determines the nature and fertility of the soil.indicates an increasing degree of soil developing and soilSoils with good aggregate structure not only has a high levelorganic matter content. Experimental results show that ag-of porosity and water holding capacity, but also good per-gregates reclaimed for 30 years are the most serious danmeability, which is conducive in providing plants with water, aged in structure. The unstable and relatively poor soilfertilizer, gas, and heat during the plant growing season.structure of the samples may be the result of short term rec-Therefore, soil aggregates have a certain significance oflamation according the study area investigation.Table 3 The composition of aggregate and its stability in the surface (0- 20 cm) and subsurface (20- 40 cm)soil layers of different reclamation years (%)(0- -20 cm)Water-stableDuration (years) ofDry aggregatesaggregateDestruction ratereclamation>5mm 5- 2mm 2-1mm 1-0.5mm 0.5- 0.25 mm_ >0.25 mm>0.25 mm4.80°8.67d4.408.67922.27*48.8049.59(0.40)(1.40)(1.00)(2.32)(3.67)12.93b12.275.93°8.87°12.53d2.534.8990.69(2.61)(3.24)(1.27)(1.86)(1.80)34.60*23.67*10.1312.47b2(91.1323.3874.34(10.02)(2.34)(1.10)(4.62)27.80*23.40*9.73b12.13b10.53d3(83.606.6392.07(3.75)(1.44) .(2.20)(2.04)(1.70)15.93b20.00'10.0018.40*20.600babout 10084.9325.6569.80(2.54)(0.35)(0.72)(1.51)(0.20)28.87*20.0068.40b13.53b16.33babout 50087.136.3558.29(9.45)(1.04)(0.92)(3.52)(5.08)17.13520.80b 10.9314.93*b15.0obedabout 1,0008.8037.07(3.06)(1.93)(1.45)(2.14)(1.31)(20- 40 cm)>5mm 5- -2mm 2- -1 mm 1- -0.5 mm 0.5 -0.25 mm >0.25 mm1.73d8.07°5.27°12.87b56.8(19.8165.12(1.15)(5.59)(3.42)(6.63)(14.84)11.738.80°4.13°5.67b40.332.3294.24(5.57)(2.69)(2.78)41.3322.53b8.60b10.73b92.1310.56 .88.54 .(15.79)(1.67)(2.23)(5.23)23.13be18.73b7.87010.4010.53b3070.662.5696.37(3.59)(6.62)(2.41) .(2.60)34.53*b22.47b8.40e10.93b88.2785.60(11.71)(6.77)(2.62)(2.81)(3.11)24.73bhe23.13b9.87b15.20*15.73b88.6722.3674.78(13.02)(0.90)(1.22)(3.98)(5.40)35.07°16.4729.53b89.2723.3373.87(3.08)(0.61)(1.60)Means with the different letter in the same row are significantly different (p<0.05) (Duncan's test): Data in the narentheses are standarddeviations. Destruction rate= [(>0.25 mm Dry aggregate)- (>0.25 mm Water-stable aggreg中国煤化工YHCNMH G350Hui Wang et al, 2010/ Sciences in Cold and Arid Regions, 2(4): 0345- -03533.3. Changes of particle composition and specific surface areaTherefore, by studying sand, silt, and clay contents,and specific surface area changes of oasis soil with thedifferent cultivation years, one can explain the process ofWith increasing cultivation years, the sand content of0- 20oasis soil texture changes. Within seven years of cultiva-cm and 20- 40 cm soil layers decreased, but silt content in-tion, sand content deceased, and silt content and specificcreased. Compared to the non-reclaimed land, after sevensurface area increased, which means that during theyears of reclamation, sand content in the 0- 20 cm layer dropsoasisization process, water-holding capacity and fertilizerfrom 85.42% to 62.46% and silt content varies from 11.33%protection ability increased. Fine particles, especially clay,to 32.64%; in the 20- 40 cm layer, sand content drops fromcontains more nutrients, coupled with an increase of the89.51% to 68.16% and silt content increases from 8. 15% tospecific surface area, results in an increase of soil nutrient27.83%. In the surface soil, clay content varies from 2.44 tocontent. Therefore, the accumulation of fine particles, un-4.80%, the soil specifc surface area (SSA) varies from 128 toder the process of man-made oasis irrigation and farming,247 cm2/g; sub-surface soil clay content varies from 3.08 toare the main reasons why clay soil texture and fertility4.3 1%, and the SSA varies from 118 to 239 cm/g (Table 4).increases in an oasis.Table 4 Mechanical composition and specific surface area (SSA) of the surface (0 20 cm) and subsurface (20- -40 cm)soil layers of dfferent reclamation yearsDuration (years)of0- -20 cmreclamationSand (%)Silt(%)Clay (%)SSA (cm-/g)85.42* (1.95)1.33(2.30)3.93*"(1.04)128 (20.67)62.46" (3.85)32.64*(4.71)3.575 (0.86)205 (32.76)51.159 (6.79)46.23* (6.50)2.44 (0.36)236 (20.63)59.78"《(12.34)36.59"(11.54)4.010(0.22)230(47.02)about 10064.04 (2.21)32.00*(4.94)3.56" (0.38)202 (13.40)about 50055.91"(2.59)42.01*(1.05)3.83 (0.65)247 (15.91)about 1,00061.56he (2.86)33.04"(2.5)4.80 (0.14)231 (11.70)Duration (years) of20- 40 cmSilt (%)SSA (cm2/g)89.51*(4.57)8.15* (3.21)4.03*(0.39)118 (18.44)68.16*(14.74)27.83h0 (14.05)3.76b (0.26)190 (54.36)45.995 (3.66)51.69*(4.35)3.08° (0.21)221 (17.56)56.31(29.09)39.13*(27.03)3.64be (0.45)232 (10.21)60.89*(.31)3.05*(1.92)3.64he (0.21)208 (4.27)57.49h (3.02)39.91*(4.51)3.81*(0.31)239 (17.99)56.46' (3.95)36.333 (3.68)4.312 (0.24)234 (12.20)Means with the different letter in the same row are significantly different (p<0.05) (Duncan's test); Data in the parentheses are standarddeviations.ter that expresses soil bulk density, porosity, aggregate3.4. Changes of saturated hydraulic conductivitystability,and mechanical composition of soil physicalproperties. Therefore, the decrease of Ksat is due to theIn the process of oasis soil development, soil saturatedformation of aggregates and soil capillary porosity duringhydraulic conductivity (Ksa) changes significantly (Tablethe oasis soil development. Related studies have pointed5). In surface and subsurface layers, Ksat reduces with in-out that in a relatively short period (10 years), soil hydrau-creasing years of reclamation. Ksat values of surface andlic conductivity values did not change significantly duringsubsurface soil layers, at the beginning (0 years), are thethe transformation from farmland to grassland (Schwardzlargest with 0.74 cm/h and 2.28 cm/h respectively. Afteret al, 2003). Our studies have shown that during the de-development of the oasis soil, Kst values decrease rapidly,velopment of soil from desert to oasis, the change of soilreduce to 0.34 cm/h and 0.13 cm/h respectively after about hydraulic con中国煤化工in a short1,000 years reclamation. Soil Ksat is an integrated parame-seven-year perioYHCNMH G .Hui Wang et al, 2010/ Sciences in Cold and Arid Regions, 2(4): 0345- 0353351Ksat has a greater standard of deviation, indicating thafirst few minutes differ widely, whereas 20 min later, theseit is stronger than the spatial heterogeneity of other soil rates gradually stabilize. Therefore, calculated Ksat can be aphysical properties. Observation data shows that in parallelreliable measurement tool, and oasis soil development im-samples, the declining rates of the reservoir water in thepacts soil physical properties.Table 5 Saturated hydraulic conductivity (Ksu) for the surface (0- 20 cm) and subsurface (20- 40 cm)soil layers of different reclamation yearsDuration (years) of reclamation0 -20 cm_20- 40 cm0.74* (0.41)2.28*(0.97)70.67*(0.22)0.41"(0.25)2(0.45'(0.22)0.640 (0.32)3(0.445 (0.29)1.20*(0.40)about 1000.24° (0.14)0.38he (0.24)about 5000.43*(0.24)0.54bx 0.33)about 1,0000.34*"(0.50)0.13° (0.06)Means with the different letter in the same row are significantly different (p<0.05) (Duncan's test); Data in the parentheses are standarddeviations.and 1.48 cm-/gyr, respectively (Table 6). Under natural3.5. The changing rate of soil physical properties in theconditions, the structure of desert soil is poor, gravel andprocess of oasis soil developmentand content is high, and large pores exist. With theman-made water irigation system, soil fertility and cropIn the initial 30 years of oasis soil reclamation, soilcultivation improved and soil properties fundamentallyphysical properties underwent relatively rapid changes, suchchanged. Thus, in the first decades of reclamation, soilas saturated hydraulic conductivity (KSsa), dry aggregates >physical properties changed significantly, reflecting an im-0.25 mm, water-stable aggregates >0.25 mm, and specificprovement of soil structure, decrease in sand content, and asurface area, which are 0.01 cm/h:yt, 0.58%/y, 0.50%/yr,decrease in Kst values.Table 6 Incremental rates (within 0 -20 cm depth) of saturated hydraulic conductivity (Ksu), >0.25 mm dry aggregateor >0.25 mm water-stable aggregate as well as specific surface areaAge groups of land reclamation (year)Physical properties0- -3030- -100100500500- 1,000saturated hydraulic conductivity (cm/h*yr)0.011032x 1045x106>0.25 mm dry aggregate (%/yr)0.580.090.027x103>0.25 mm water- stable aggregate (%/yr)0.500.076x103specific surface area(cm/g:yr)1.480.220.051.8x102Ksat. SSA is mainly affected by dry aggregates >0.25 mm.3.6. Correlation analysis of oasis soil physical propertiesKsat is negatively correlated with SSA, dry aggregates>0.25 mm, and water-stable aggregates >0.25 mm, but isSoil bulk density is negatively correlated with most soilpositively correlated with sand content, indicating thatphysical properties at the 0- -20 cm layer, such as total po-improvement of the soil structure is the main factor caus-rosity, capillary porosity, specific surface area SSA, anding the reduction of the saturated hydraulic conductivitywater- stable aggregates >0.25 mm (Table 7). Increase ofKstr Correlation analysis shows that the soil water-holdingsoil porosity has a close relationship with clay content,capacity is strongly correlated with bulk density and poros-SSA, and water-stable aggregates >0.25 mm. With theity. Also, the soil water-holding capacity is positively cor-increase of reclamation years, soil sand content and otherrelated to clay, SSA, and water-stable aggregates >0.25soil physical properties are related. For example, soil sandmm, indicating that with development of the oasis soil andcontent has a significant negative correlation with SSA andthe improvemer中国煤化工r-holding ca-dry aggregates >0.25 mm, but is positively correlated withpacity increases.MHCNMH G .352Hui Wang et al, 2010/ Sciences in Cold and Arid Regions, 2(4): 0345- 0353Table 7 Correlation of main soil physical properties in the surface (0- 20 cm) soil layer of diferent years of reclamationDAWAPhysicalBDIPCISand Clay SSA(>0.25 (>0.25)RKMWC FWCpropertiesmm) mm)P-0.94" 0.91*0.36Clay-0.270.300.47 0.36 1Ss.-0.47 0.490.40 - 0.96* -0.10 1DA(>0.25 mm)-0.14 0.190.13-0.78*- - 0.23 0.79*WA(<>0.25 mm)-0.520.480.55-0.040.41 0.18DR0.43. -0.39. -0.48 -0.35 - 0.490.20 0.03 - 0.92* 1Ka-0.05 0.06-0.04 0.56- -0.09- 0.62- 0.84° - 0.44 0.131MWC .-0.97** 0.95**0.99**-0.300.450.10.57-0.48 .-0.05WC-0.87*-0.500.44BD: bulk density; TP: total porosity; CP: caillary porosity; SSA: special surface area; DA: dry aggregate; WA: watr-stable aggregate; DR:destruction rate; MWC: maximum water-holding capacity; FWC: field water-holding capacity. *p<0.05, **p<0.01.4. Concusionbulk density gradually reduced with the increased of soilreclamation years is the most important symbol.(1) During the oasis soil development and expansion inZhangye, the soil physical properties improved with an in-REFERENCEScrease of soil reclamation time and the gradual aging of thesoil. With man-made irigtion-siltation and farming sludgeChen EF, 1990. The Material Basis and Control of Soil Fertility. Sciencefertilizer, soil structure was improved, soil bulk density de-Press, Beijing.creased, total porosity and capillary porosity increased, wa-Chen LH, 1982. The opinion on clasification of imigation-warping soils ofter-holding performance and the stability of soil aggregatesHexi Corridor, Gansu Province. Compiling by Soil and Ferilizer ScienceSociety of Gansu Province.enhanced, and saturated hydraulic conductivity decreased.Chen LH, Di XM, Li FX, 1993. aification of Oasis Soil in Hexi Corridor.The development and evolution of the oasis soil include theScience Press, Bejing.underlying reasons of the natural properties determined byFan HW, Jia XH, Zhang JG Ma FY, Li XR, 2002. Influence of soil degrada-tion and desertification on soil carbon cycling in arid zones. Joumal ofthe system itself, and more important is the participation ofDesert Research, 22(6): 525- -533.man-made actities. In the process of oasisization, the re- Foster GR, Young RA, Neibling WH, 1985. Sediment composition forsults of oasis soil development are more richness and morenon-point source pllution analyses. Transactins of the ASAE, (28):suitable for farming.Fu BJ, Chen LD, 2000. Agricultural landscape spatial pattem analysis in the(2) The saturated hydraulic conductivity, dry aggregatessemi-arid hill area of the Loess Plateau, China. Joumal of Arid>0.25 mm, water-stable aggregates >0.25 mm, and the sur-Environments, 44(3): 291- -303.face area underwent relatively rapid change in the initial 30 Fu BJ, Wang J, Chen LD, Qiu Y, 2003. The efects of land use on soilyears of soil reclamation, which are 0.01 cm/h:yr, 0.58%/yr,moisture variation in the Danangou catchment of the Loess Plateau,China. Catena, 54(1- 2): 197- -213.0.50%/yr, and 1.48 cm/g:yr, respectively.(3) The increase of soil porosity is closely related to clayGuo YR, Zhao HL, Zhao XY, Zuo X, Luo YY, 2007. Crust development andits infuences on soil physicochemical properties in arifcial forest ofcontent, SSA, and water stable aggregates >0.25 mm. SandHorqin Sand Land. Joumal of Desert Research, 27(6): 1000 -1006.content is most significantly negatively and significantlyInstitute of Soil Science, Chinese Academy of Sciences (ISSCAS), 1978.The analysis of soil physicochemistry properties. Shanghai Scientiic andnegatively correlated with SSA and dry aggregates >0.25Technical Publishers, Shanghai. 7- -59.mm and positively correlated with the saturated hydrauliclia BQ, Ci LJ, 2003. Oasis Landscape Ecological Study. Science Press,conductivity Ksat. Soil specfic surface area (SSA) is mainlyBeijing.affected by dry aggregates >0.25 mm; saturated hydraulicLi FX, 1995. A study on imigation-warping soils of oases in Hexi Coridor,Gansu Province. Journal of Arid Land Resources and Environment, 9(4):conductivity Ksat is negatively correlated with SSA, dry ag-180-186.gregates >0.25 mm, and water stable aggregates >0.25 mm.Li FX, Chen LH, Zhao FH, Wang LB, 1999. The characteristic and casfi-Soil water-holding capacity is positively correlated with clay,cation reference of irigation-warping soils of oases in Hexi Corridor,SSA, and water-stable aggregates >0.25 mm. Soil bulk den-Gansu Province. Soil, (4): 202- -207.Li YB, Xie DT, 2001. Features of water-stable soil aggregate structure undersity is negatively correlated with the majority of soil physi-cal properties. In all soil physical properties studied, the soildiffrerent land us中国煤化工and Water Comservation, 15(4):MYHCNMH G .Hui Wang et al, 2010/ Sciences in Cold and Arid Regions, 2(4): 0345- 0353353Liu LW, Zhou JM, Liu DS, 2000. Genesis and evolution of chestnut soils inWu CZ, Hong W, 1999. Study on fractal features of soil aggregate structurethe altermative belt of semiarid agriculture and animal husbandry. Actaunder different management patterms. Acta Pedologica Sinica, 36(2):Pedologica Sinica, 37(2): 174 -181.162- -167.Luo GP, Xu WQ, Chen X, 2005. Effect of different land-use systems on soilXiao HL, Zhao X, Zhao WZ, 1998. Study on Uap-Ustic Isohumisol degra-properties in the alluvial plain-oasis in the arid land. Acta Geographicadation under farming in Hebei, China. Acta Pedologica Sinica, 35(1):Sinica, 60(5): 779- -790.129- -134.Ma FY, Li XR, Zhang JG Li AX, 2005. Spatial heterogeneity of soil physicalXu wQ, Luo GP, Chen X, Xiao LX, 2006. Spatio-temporal variability of soilproperties in Shapotou artificial sand-fixing vegetation area. Journal oforganic C and nutrients in the oasis of the northerm slope of the TianshanDesert Research, 25(2): 207- -215.Mountains. Geographical Research, 25(6): 1013- -1021Pan XD, Wang MF, He X, Wang K, Li YM, Zhang S, Zhang FH, 2005. TheYan XS, 1988. The Research Methods of Soil Fertility. Science Press, Bei-successional trend of soil quality after reclamation in the oasis of Manasijing.River Valley. Chinese Agricultural Science Bulletin, 21(8): 377- -379.Zeng YN, Feng ZD, 2008. Effect of desetification on soil organic carbonSchwardz RC, Evett SR, Unger PW, 2003. Soil hydraulic properties of crop-pool of grassland in headwater area of Yellow River. Journal of Desertland compared with reestablished and native grassland. Geoderma, 116:Research, 28(2): 208- 211.Zhang FH, Pan XD, Li YY, 2006. Research on successional regulation ofShi CH, Gong ZT, 1992. Oasis Soil Genesis and Taxonomy. Science Press,soil environment after reclamation in the Manas River Valley. ScientiaBeijing. 25- 33.Agrcultura Sinica, 39(2): 331- -336.Shi CH, Gu GA, 1991. Oasis soils in China. Arid Zone Research, 8(4); 1-9.Zhang MK, He ZL, Chen GC, Huang CY, 1997. Formation of water-stableStolte J, van Venrooii B, Zhang G Trouwbrost KO, Liu GB. Ritsema CJ.aggregates in red soils as affected by land use. Acta Pedologica Sinica,Hessel R, 2003. [ and use induced spatial heterogeneity of soil hvdraulic34(4): 359 -366.nroperiesontheI ess plateauinChina Catena 54.59- 75Zhao HL, Huang XW, He ZY, 1996. Research on successional trend of theSuYZ, Zhao HL, Zhang TH, Cui JH, 2002. Characteristis of sandydesertification process of the farmland in Horqin Sandy Land. Acta Pe-grassland soils under post-grazing natural restoration in Horgqin Sandydologica Sinica, 33(3): 242- -248L and. Journal ofDesert Research. 22(4): 333 338.Zhao HL, Zhao XY, Zhang TH, Li YL, Su YZ, 2002. Study on bio-pocessesSun HL, Liu GS, 1996. The Analysis of Soil Physicochemistry Propertiesin desertification in northern agro-pasture interzone. Journal of Desertand Descriptions on Profles. Standards Press ofChina. Beiing,Research, 22(4): 309- 315.Wang JZ, 1984. The oasis soil of imigated area with Yellow River in Ningxia.Zhao WZ, Xiao HL, Liu ZM, Li J, 2005. Soil degradation and restoration asActa Pedologica Sinica, 22(4): 434 -437.affected by land use change in the semiarid Bashang area, northern China.Wen Q, Zhao XR, Chen HW, Tuo DB, Lin QM, 2004. Distribution charac-Catena, 59(2): 173- 186.teristics of microbial biomass cartbon in different soil aggregates insemi-arid area. Scientia Agricultura Sinica, 37(10): 1504 -1509.中国煤化工YHCNMH G